The present invention relates to a magnetic film, which can be applied to a magnetic head, etc., a magnetic head and a solid device, which include the magnetic film.
Recording density of hard disk drive units is increasing 100% every year. To maintain the increasing rate from now on, resolution of a recording head in a direction of gap length must be improved, further width of an element of the head in a direction of track width must be smaller. In conventional recording heads, it is important to make a clearance between the recording head and a recording medium smaller so as to improve the resolution of the recording head, further it is also important to make the width of the element of the head smaller.
Conventional recording heads of hard disk drive units are shown in FIGS. 10 and 11. FIG. 10 shows a conventional head for longitudinal magnetic recording; FIG. 22 shows a conventional head for perpendicular magnetic recording. In each of the conventional recording heads, an electric current runs through a coil 5, which is made of a metallic film having small resistance, e.g., copper film, so that a magnetic field is induced in the coil 5 by Ampere's law. The induced magnetic field is converged in a magnetic pole, which is made of a magnetic film having high magnetic permeability, and a high density magnetic field is generated so that magnetic patterns can be recorded in a recording medium 10.
In the recording head for longitudinal magnetic recording, an upper magnetic pole 6 and a lower magnetic pole 7 constitute a closed magnetic circuit with a recording gap; in the recording head for perpendicular magnetic recording, only a main magnetic pole 8 constitutes an opened magnetic circuit.
In the recording head shown in FIG. 10, a reproducing head 4, which faces on the recording medium 10, is located at a position between the lower magnetic pole 7 and a lower shield 9. On the other hand, in recording head shown in FIG. 11, a reproducing head 4, which faces on the recording medium 10, is located at a position between a return yoke 11 and a lower shield 9. With these structures, the magnetic heads are capable of recording data in and reproducing data from the recording media 10.
To record magnetic patterns in the recording medium 10, the magnetic pole or poles are moved closed to the recording medium 10, which is made of a magnetic material having a great coercive force, then an electric current having an optional wave form runs through the coil 5 so as to irradiate the magnetic field toward the recording medium 10. At that time, the recording medium 10 is rotated so as to record magnetic patterns in the recording medium 10 according to polarities of the current running through the coil 5.
In this recording method, a size of the head must be smaller than the magnetic patterns so as to increase recording density. When the magnetic patterns are made smaller, the magnetic pole or poles of the head sometimes project.
These days, with increasing the recording density, intensity of a recording magnetic field of a hard disk drive unit is several hundred kA/m. To increase the intensity of the recording magnetic field, it is effective to increase intensity of the current running through the coil 5, but Joule heat also increased. Further, eddy currents are generated when the induced magnetic field passes the magnetic pole, so that the head is further heated. The heat generated in the head expands the upper magnetic pole 6 or the main magnetic pole 8, and alumina around the magnetic pole, so that the magnetic pole projects. In FIG. 12, the magnetic pole projects toward the recording medium 10 by the heat of the recording head.
If the magnetic pole of the recording head projects toward the recording medium 10, the recording magnetic field is deformed, and magnetic patterns cannot be correctly recorded in the recording medium 10. Further, in the worst case, the head contacts the recording medium 10 so that the both are damaged. To prevent the interference between the both, a clearance is formed between the recording head and the recording medium 10 with considering the projection of the magnetic pole. However, a reproducing head 4, which is provided in a plane including the recording head, is separated away from the recording medium 10, so that resolution of the reproducing head 4 must be lowered.
Therefore, even if narrow magnetization patterns are recorded on the recording medium, the reproducing resolution is insufficient, so total recording density of the hard disk drive unit cannot be increased.
These days, a projecting length of a magnetic pole, which is projected by heat of the recording head, is about 5 nm. On the other hand, a clearance between the magnetic pole and the recording medium has been very small, e.g., 10-15 nm. It is necessary for increasing the recording density to make the clearance smaller. Therefore, limiting the projection of the magnetic pole is the most important subject.
On the other hand, it is necessary for a material of the magnetic pole to generate a magnetic field of several hundred kA/m, so a material having great saturation magnetization (Bs) or good soft magnetic characteristics as the material of the magnetic pole. For example, a Fe70CO30 alloy, an alloy including Fe70CO30 and other metal(s), a chemical compound of the Fe70CO30 alloy, a CoNiFe alloy, a Fe50CO50 alloy, an alloy including Fe50CO50 and other metal(s), and a Ni81Fe19 alloy, which are arranged in order of the value of the saturation magnetization (Bs). However, these materials have a positive coefficient of thermal expansion, so that the magnetic pole is projected. Coefficients of linear thermal expansion of the materials are shown in TABLE 1.
TABLE 1COEFFICIENT OF LINEARSATURATIONTHERAMAL EXPANSIONMAGNETIZATIONMATERIAL[×10−6K−1][T]Fe70Co3028.22.4Ni50Fe5010.01.6Ni81Fe1912.41.0Cu16.40Alumina6.8-12.20Fe64Co363.50.8Fe66Pd341.60.8Fe73Pt27−301.0
The coefficient of linear thermal expansion indicates a ratio of expansion in one direction when temperature of the material rises 1° C. For example, the coefficient of linear thermal expansion of Fe70CO30 is 28.2×10−6·K−1. Namely, if temperature of the Fe70CO30 alloy, whose size is 10 mm×10 mm, rises +1° C. one degree, the alloy expands to the size of 10.0141 mm×10.0141 mm. These days, a length of a magnetic poles of a recording head is about μm. When an electric current running through a coil generates heat and temperature of an element rises +50° C., the magnetic pole made of the Fe70CO30 alloy totally extends 14.1 nm. Namely, the magnetic pole extends 7 nm toward the recording medium. According to this example, the magnetic pole projects about 5 nm as described above. Therefore, the length of projecting the magnetic pole can be limited by employing a material having a small coefficient of linear thermal expansion.
An inver alloy has been known as a material having a small coefficient of linear thermal expansion. For example, a Fe64CO36 alloy, a Fe66CO34 alloy and a Fe73CO27 alloy are well known as the inver alloys. By employing the inver alloy as a magnetic pole of the recording head, the projection length of the magnetic pole can be reduce to one-tenth of the projection length of the conventional magnetic pole made of the Fe70CO30 alloy. However, saturation magnetization of the inver alloys are very small, e.g., 1.0 T, and their soft magnetic characteristics are insufficient, so they have not been used for magnetic poles.